This invention relates to a method and an apparatus for monitoring an ability to remove impurities of an ion adsorption apparatus using ion exchange substances, etc., and particularly to a method and an apparatus for monitoring a desalting unit suitable for continuous monitoring of an ability to remove radioactive ion species of a desalting unit in a reactor cleaning system of an atomic power plant.
It has been mentioned as a cause for increasing the dose rate of radiation in commercial atomic power plants that a very small amount of various ion species such as Co ions, Ni ions, Fe ions, etc. discharged from the materials of construction in the primary cooling system are deposited on the surfaces of fuel rods, and are made racioactive through exposure to neutron irradiation, and the radioactive ion species such as .sup.60 Co ions, .sup..quadrature. Co ions, .sup.54 Mn ions, etc. are released from the fuel rods and deposited on the surfaces of pipings outside the reactor core, as disclosed, for example, in "Boshoku Gizitsu (Anticorrosion Technology)" Vol. 32, pages 276-285 (1983). Thus, it has been proposed to provide a desalting unit with ion exchange resin to remove such radioactive ion species from the core water (the desalting unit may be hereinafter referred to as "desalting unit in a reactor cleaning system"). The desalting unit in a reactor cleaning system has played an important role in prevention of an increase in the radiation dose rate in the atomic power plant.
Heretofore, monitoring of an ability to remove the radioactive ion species of a desalting unit in a reactor cleaning system has been carried out by sampling core water at the inlet and the outlet of the desalting unit and measuring concentrations (on ppm level) of ion species playing an important role in the radiation dosage rate in the plant, for example, concentrations of .sup.60 Co ions, etc., thereby detecting deterioration of the removal ability, for example, the ability of the desalting unit through a decrease in the ratio of .sup.60 Co ion concentration between the inlet and the outlet of the desalting unit. However, the conventional method requires 40 to 80 l of sampling water for measuring concentrations of impurity ion species on a ppm level, but the actual sampling rate is about 0.1 l/minute, and thus the required sampling time is inevitably prolonged to, for example, about 10 hours and rapid measurement is hard to conduct. Furthermore, sampling of core water is usually carried out once in a week, but the actual analysis of the sampled core water is carried out about one week after the sampling, because it is necessary to decay the radioactivity of radioactive nuclear species having a shorter half life in the sampled core water thoroughly to lower the background level. That is, it takes maximum two weeks from the start of .sup.60 Co ion leakage from the desalting unit to the actual detection. Thus, the radioactive ion species playing an important role in the radiation dosage rate in an atomic power plant, such as .sup.60 Co ions, etc. are concentrated and accumulated in the core water, resulting in an increase in the radiation dosage rate.